1. Field of the Invention
The present invention relates to a method for subjecting a trim cover assembly to foaming by injecting and curing a liquid foaming material therein, to thereby form a foamed product integral with the trim cover assembly, such as a headrest or armrest for use with an automotive seat.
2. Description of Prior Art
Seats, headrests, armrests and other cushiony accessories for use in automobiles are basically formed from a trim cover assembly and a foam cushion member. In particular, a typical process for forming a relatively small article, such as headrest or armrest, involves a foaming step wherein a liquid foaming material is injected and cured in a three-dimensional trim cover assembly to create a foam cushion member filled therein, together with a framework and some fittings if required, so as to produce a resulting foamed product integral with the trim cover assembly (e.g. headrest or armrest). In most cases, the three-dimensional trim cover assembly used is preformed by sewing together plural separate cover sections, each comprising a top cover layer (or surface cover piece) and a thin foam layer (or slab foam wadding piece), into a predetermined three-dimensional or box-like configuration that conforms to an outer shape of a resulting product.
In this kind of trim cover assembly, a natural or artificial leather material is sometimes required as the top cover layer thereof. Typically, the natural leather material includes a bull leather, a horse leather or the like, and the artificial leather material includes a synthetic resin leather or the like. In that instance, conventionally, a piece of leather surface cover material, be it of a natural or artificial leather, is adhesively laminated at its reverse side to one piece of thin foam padding to create one cover section unit which forms a part of a resulting three-dimensional trim cover assembly. However, in this particular lamination process, an adhesive is applied to whole areas of both leather surface cover piece and foam padding piece to thereby provide a bonded cover section unit. Such bonded cover section unit will inevitably cause objectionable wrinkles and creases therein when it is bent and curved by a worker for sewing with another bonded cover section unit (s). Further, in most cases, a plurality of the thus-bonded cover section units are first set in a reversed state where the foam padding layers thereof are exposed outwardly, and then, they are sewn together to form a reversed state of three-dimensional trim cover assembly (generally conforming to an outer shape of headrest or armrest, for instance) wherein all the foam padding layers are exposed outwardly while the leather surface cover layers are situated in the interior of trim cover assembly. Then, such reversed trim cover assembly is turned over from an opening thereof into an normal state where all the leather surface cover layers are exposed outwardly. This reversing process further causes additional wrinkles and creases in the resultant trim cover assembly, which impairs the aesthetic appearance of leather surfaces thereof.
To solve the problem, instead of the foregoing full lamination, it has been proposed to effect a partial connection between the leather surface cover piece and foam padding piece. That is, the peripheral end regions of the leather surface cover piece are adhesively attached or sewn along and with the corresponding peripheral terminal ends of foam padding piece to form a partially joined cover section unit. But, when a plurality of such cover section units undergo the abovementioned bending and curving step while sewing them together and also undergo the reversing process for reversing the trim cover assembly into a normal state, the foam wadding layers are floated and waved from the leather surface layers, thus creating plural creased and bent areas in the foam wadding layers. Eventually, when subjecting the thus-formed trim cover assembly to a foaming process, there are a plurality of incompletely foamed spots at those creased and bent areas in the foam wadding layers.
In view of the above-stated drawbacks, it is therefore a primary purpose of the present invention to provide an improved method for forming a foamed product integral with trim cover assembly which insures to avoid creation of slack and crease in both of surface cover pieces and foam padding pieces of the trim cover assembly.
In order to attain such purpose, in accordance with the present invention, there is basically provided a method comprising the steps of:
forming a plurality of surface cover pieces in a predetermined shape, each having ends;
forming a plurality of foam padding pieces, each being generally equal in size to each of the plurality of surface cover pieces;
temporarily securing local points of each of the plurality of foam padding pieces to the respective local points of each of the plurality of surface cover pieces via a securing means, thereby providing a temporarily secured cover section unit;
providing a plurality of such temporarily secured cover section units;
thereafter, sewing together end portions of the plurality of the temporarily secured cover section units, thereby forming the trim cover assembly in a three-dimensional shape;
injecting a liquid foaming material into inside of the thus-formed trim cover assembly;
curing and expanding the liquid foaming material so as to create a foam cushion member filled in the trim cover assembly; and
thereafter, removing the local points of each of the plurality of the cover surface pieces from the respective local points of each of the plurality of the foam padding pieces, overcoming a securing strength of said securing means;
whereby the foamed product integral with the trim cover assembly is formed, in which both surface cover pieces and foam padding pieces are stretched uniformly.
Accordingly, due to such scattered temporarily secured points, there is no restrained relation between the surface cover piece and the foam padding piece all through the assembly processes, which insures to allow free relative stretching movement between the two layers by removing the local points therein after the foaming process, whereby any crease and slack is not caused in both of the layers in a resultant foamed product. Hence, the outer aesthetic appearance of the foamed product, such as a headrest or an armrest, is far improved. This is particularly effective in the case of the surface cover piece being a natural or artificial leather material.
Preferably, the aforementioned local points for temporarily securing may be defined adjacent to and along the end portions of each of the plurality of surface cover pieces and foam padding pieces, and the peripheral ends of the temporarily secured cover section unit may be sewn together along a line distant from said local points, prior to providing a plurality of said temporarily secured cover section units.
Other various features and advantages will become apparent from reading of the descriptions hereinafter, with reference to the annexed drawings.